The following green pellets and the like are conventionally known. Specifically, one is a green pellet comprising an inner core layer 111 in which an iron ore powder, a carbonaceous material, and a lime-based auxiliary starting material are mixed with each other, a first coating layer 112 which covers the inner core layer 111 and which is made of an iron ore powder, and a second coating layer 113 which covers the first coating layer 112 and which is made of a carbonaceous material (see FIG. 3A), as described in Patent Literature 1 listed below and the like and proposed as production of partially reduced iron by use of a sintering machine. Another is a green pellet having a coating layer 122 containing CaO at 25% by weight or more and being disposed on a surface of a particulate body 121 in which a powdery iron starting material and a powdery solid reducing agent are mixed with each other, as described in Patent Literature 2 listed below and the like (see FIG. 3B).
Suppose a case where the conventional green pellet 110 described in Patent Literature 1 listed below and the like is supplied to a partial reduction furnace of a packed bed-type such as a sintering machine. In such a case, the lime-based auxiliary starting material in the inner core layer 111 forms a calcium ferrite-based melt, as the combustion of the carbonaceous material proceeds. Part of the melt oozes so as to be absorbed into the iron ore powder in the first coating layer 112, and partially melts the iron ore powder in the first coating layer 112. The rest of the iron ore powder in the first coating layer 112 is calcined, and a dense solidified layer surrounding the inner core layer 111 is formed after the calcination. Consequently, a pellet can be obtained which is prevented from reoxidation due to a reaction of the partially reduced iron with oxygen in the air.
Meanwhile, suppose a case where the conventional green pellet 120 described in Patent Literature 2 listed below and the like is supplied to a partial reduction furnace. Also in such a case, CaO in the coating layer 122 functions as a flux for forming a low-melting compound, and forms a melt layer by a reaction with iron. Thus, a pellet can be obtained which is prevented from reoxidation by blocking the contact of iron with supplied air.